Birth of a Microemulsion

Computers, cars, cell phones. Lately it seems that when consumers are looking to buy new toys, the hottest, fastest and most advanced technology comes in the smallest packages. Slim-line laptops, speedy foreign cars and mobile phones that nearly get lost in purses and pockets are all the rage these days – but who knew pesticides were the same way?

Keith Parker did. As a staff chemist for Syngenta Professional Products, Greensboro, N.C., Parker and a team of formulation chemists are challenged regularly to create pesticides with maximum performance.  The way to do this, they found, was to reformulate the pesticides’ active ingredients to create solutions in which the chemicals are suspended in water and nearly invisible.

“Most pure chemicals are hydrophobic,” Parker comments. “Literally, that means they’re afraid of water. You can see by pouring compounds like propiconazole into water, they’re just not going to mix.”

With emulsion technology – used in everything from food to cosmetics – chemists add inert ingredients to the original chemical to make them “hydrophilic” or “water-loving.” These ingredients don’t change the chemical make-up of the active ingredient, but simply allow it to mix with water for a short period of time.

“Even at this stage, though, mixing the [water and active ingredient] together only lasts for a little while as a simple emulsion,” Parker notes, and suggests thinking of the resulting solution as similar to Italian salad dressing. A bottle of Italian dressing will separate back into oil and water not long after you drizzle it over your food, and pesticides at this stage are the same way.

How do pesticide manufacturers solve this problem?

“Imagine taking something to craft a bridge between the oil and the water,” Parker says. “You need another molecule that’s half hydrophobic to attach to the oil and half hydrophilic to attach to the water.” These ingredients, called surfactants, keep the oily active ingredient particles from reconverging. “When they’re surrounded by surfactants, two oil droplets will not combine,” Parker notes. “Each new molecule also has a small electrical charge which causes them to repel each other like two magnets.”

With the right surfactants and inert ingredients added in the correct amounts, concentrated active ingredients form microemulsions in water, which can ultimately benefit the pesticide applicator.

“Products like these can be held longer since they are indefinitely stable unless they’re mixed with other products,” Parker comments. “There is also empirical evidence that microemulsions act better in spray tanks since they won’t separate and they’re also easier on equipment seals.” Additionally, by including surfactants in the pesticide recipe, there is evidence that microemulsions may actually stick better to plants and, therefore, work more effectively. (See “A Sticky Situation” for more information on how surfactants work in pesticides.)

Though it can take three to four years to develop a new formulation, Parker and other chemists are working on products right now to make them available to applicators as soon as possible.

The author is Assistant Editor of Lawn & Landscape magazine and can be reached at lspiers@lawnandlandscape.com.